move call to update_templates on service startup into a django-admin command

cms/djangoapps/contentstore/__init__.py

@@ -1,3 +1 @@
-from xmodule.templates import update_templates
 
-update_templates()

rakefile

@@ -440,6 +440,13 @@ namespace :cms do
   end
 end
 
+namespace :cms do
+  desc "Imports all the templates from the code pack"
+  task :update_templates do
+    sh(django_admin(:cms, :dev, :update_templates))
+  end
+end
+
 namespace :cms do
   desc "Import course data within the given DATA_DIR variable"
   task :xlint do